The European Union Emissions Trading Scheme (EU ETS) has imposed a price on the allowances for CO2 emissions of electricity companies. Integrating this allowance price into the price of electricity earns a rent for companies who have received these allowances for free. During Phase I, 2005–2007, rents corresponding to the aggregate value of allocated allowances amounted to roughly € 13 billion per year. However, due to the specific price-setting mechanism in electricity markets true rents were considerably higher. This is due to the fact that companies also that have not received any allowances gain additional infra-marginal rents to the extent that their variable costs are below the new market price after inclusion of the allowance price. Producers with low carbon emissions and low marginal costs thus also benefit substantially from carbon pricing. This paper develops a methodology to determine the specific interaction of the imposition of such a CO2 constraint and the price-setting mechanism in the electricity sector under the assumption of marginal cost pricing in a liberalized European electricity market. The article thus provides an empirical estimate of the true total rents of power producers during Phase I of the EU-ETS (2005–2007). The EU ETS generated in Phase I additional rents in excess of € 19 billion per year for electricity producers. These transfers are distributed very unevenly between different electricity producers. In a second step, the paper assesses the impact of switching from free allocation to an auctioning of allowances in 2013. We show that such a switch to auctioning will continue to create additional infra-marginal rents for certain producers and will leave the electricity sector as a whole better off than before the introduction of the EU ETS.